Soil remediation with heated soil

ABSTRACT

Methods are provided for remediating contaminated soil. The methods may include collecting contaminated soil at a plurality of treatment sites. The contaminated soil at one or more of the plurality of treatment sites may be at least partially contained. The method may include heating soil at a first site with a plurality of heat sources to substantially reduce contamination of the soil at the first site. Soil at a second site may be heated using a plurality of heat sources. A portion of vapors produced from the second site may be allowed to enter the substantially uncontaminated first site. Contaminants within the portion of vapors produced from the second site may be at least partially destroyed at the first site.

BACKGROUND

1. Field of the Invention

The present invention generally relates to soil remediation systems andmethods. Embodiments of the invention relate to systems and methods ofusing heated, substantially uncontaminated soil at a first site todestroy contaminants within a portion of vapors produced fromcontaminated soil at a second site.

2. Description of Related Art

Soil contamination is a matter of concern in many locations. “Soil”refers to unconsolidated and consolidated material in the ground. Soilmay include natural formation material such as dirt, sand, and rock, aswell as fill material. Soil may be contaminated with chemical,biological, and/or radioactive compounds. Contamination of soil mayoccur in a variety of ways, such as material spillage, leakage fromstorage vessels, and landfill seepage. Public health concerns may ariseif contaminants migrate into aquifers or into air. Soil contaminants mayalso migrate into the food supply through bioaccumulation in variousspecies in a food chain.

There are many ways to remediate contaminated soil. “Remediating soil”means treating the soil to reduce contaminant levels within the soil orto remove contaminants from the soil. An ex situ method of remediatingcontaminated soil is to excavate the soil and then process the soil in aseparate treatment facility to reduce contaminant levels within the soilor to remove contaminants from the soil. Alternatively, contaminatedsoil may be remediated in situ.

Thermal desorption is a soil remediation process that may involve insitu or ex situ heating of contaminated soil. Heating the soil mayreduce soil contamination by processes including, but not limited to,vaporization and vapor transport of contaminants from the soil,entrainment and removal of contaminants in water vapor and/or an airstream, thermal degradation (e.g., pyrolysis), and/or conversion ofcontaminants into non-contaminant compounds by oxidation or otherchemical reactions within the soil. During thermal remediation, a vacuummay be applied to the soil to remove off-gas from the soil. Vacuum maybe applied at a soil/air interface or through collection ports (e.g.,vacuum or vapor extraction wells) placed within the soil. The vapors mayentrain volatile contaminants and carry these contaminants toward thevacuum source. Vapors removed from the soil by the vacuum may includecontaminants from the soil. The vapors may be transported to a treatmentfacility. The vapors removed from the soil may be processed in thetreatment facility to remove contaminants from the vapors or to reducecontaminant levels within the vapors.

Soil may be heated by methods including, but not limited to, radiativeheating, conductive heating, radio frequency heating, and/or electricalresistivity heating. For shallow contaminated soil, a thermal blanketplaced on top of the soil or heaters placed horizontally in trencheswithin the contaminated soil may be used to apply heat to the soil.Shallow contaminated soil includes soil contamination that does notextend below a depth of about 1 m to about 2 m. For deeper contaminatedsoil, heater wells or heater/vapor extraction wells may be used to applyheat to the soil.

A vacuum may be applied to remove vapors from contaminated soil. U.S.Pat. No. 4,984,594 issued to Vinegar et al., which is incorporated byreference as if fully set forth herein, describes an in situ thermaldesorption (ISTD) process for soil remediation of low depth soilcontamination. U.S. Pat. No. 5,318,116 issued to Vinegar et al., whichis incorporated by reference as if fully set forth herein, describes anISTD process for treating contaminated subsurface soil with conductiveheating.

Heat added to contaminated soil may raise a temperature of the soilabove vaporization temperatures of soil contaminants. If soiltemperature exceeds a vaporization temperature of a soil contaminant,the contaminant may vaporize. A vacuum may be used to draw the vaporizedcontaminant out of the soil. The presence of water vapor may result invaporization of less volatile contaminants at or near the boiling pointof water. Heating the soil to a temperature below vaporizationtemperatures of contaminants may also have beneficial effects.Increasing soil temperature may increase a vapor pressure ofcontaminants in the soil and allow a vacuum system to remove a greaterportion of contaminants from the soil than possible at lower soiltemperatures. Evaporation of contaminants into air or water vaporstreams may be enhanced by heating. Heat applied to the soil may alsoresult in the destruction of contaminants in situ.

U.S. Pat. No. 5,190,405 issued to Vinegar et al., which is incorporatedby reference as if fully set forth herein, describes an in situ methodfor removing soil contaminants using thermal conduction heating andapplication of a vacuum.

U.S. Pat. No. 5,229,583 issued to van Egmond et al., U.S. Pat. No.5,233,164 issued to Dicks et al., and U.S. Pat. No. 5,221,827 issued toMarsden et al., all of which are incorporated by reference as if fullyset forth herein, describe surface heating soil remediation systems.

U.S. Pat. No. 6,824,328 to Vinegar et al. and U.S. Pat. No. 6,632,047 toVinegar et al., both of which are incorporated by reference as if fullyset forth herein, describe heater elements placed horizontally withintrenches in the soil for remediation.

U.S. Pat. No. 5,553,189 issued to Stegemeier et al., which isincorporated by reference as if fully set forth herein, describes ashallow pit for remediating near surface soil contamination.

U.S. Pat. No. 5,249,368 issued to Bertino et al., which is incorporatedby reference as if fully set forth herein, describes a sealed roll-offcontainer for contaminated soil.

A soil remediation system may include four major systems. The systemsmay be a heating and vapor extraction system, an off-gas collectionpiping system, an off-gas treatment system, and instrumentation andpower control systems.

A heating and vapor extraction system may be formed of wells insertedinto the soil for deep soil contamination or of thermal blankets forshallow soil contamination. A combination of wells and thermal blanketsmay also be used. For example, thermal blankets may be placed atcentroids of groups of wells. The thermal blankets may inhibitcondensation of contaminants near the soil surface. Soil may be heatedby a variety of methods. Methods for heating soil include, but are notlimited to, heating substantially by thermal conduction, heating byradio frequency heating, or heating by electrical soil resistivityheating. Thermal conductive heating may be advantageous becausetemperature obtainable by thermal conductive heating is not dependent onan amount of water or other polar substance in the soil. Soiltemperatures substantially above the boiling point of water may beobtained using thermal conductive heating. Soil temperatures of about100° C., 200° C., 300° C., 400° C., 500° C. or greater may be obtainedusing thermal conductive heating.

Wells may be used to supply heat to the soil and to remove vapor fromthe soil. The term “wells” refers to heater wells, vapor extractionwells, and/or combination heater/vapor extraction wells. Heater wellssupply thermal energy to the soil. Vapor extraction wells may be used toremove off-gas from the soil. Vapor extraction wells may be connected toan off-gas collection piping system. A vapor extraction well may becoupled to a heater well to form a heater/vapor extraction well. In aregion adjacent to a heater/vapor extraction well, air and vapor flowwithin the soil may be counter-current to heat flow through the soil.The heat flow may produce a temperature gradient within the soil. Thecounter-current heat transfer relative to mass transfer may expose airand vapor that is drawn to a vacuum source to high temperatures as theair and vapor approaches and enters the heater/vapor extraction well. Asignificant portion of contaminants within the air and vapor may bedestroyed by pyrolysis and/or oxidation when the air and vapor passesthrough high temperature zones surrounding and in heater/vaporextraction wells. In some soil remediation systems, only selected wellsmay be heater/vapor extraction wells. In some soil remediation systems,heater wells may be separate from the vapor extraction wells. In someembodiments, heaters within heater wells and within heater/vaporextraction wells may operate in a range from about 650° C. to about 870°C.

Thermal conductive heating of soil may include radiatively heating awell casing, which conductively heats the surrounding soil. Coincidentor separate source vacuum may be applied to remove vapors from the soil.Vapor may be removed from the soil through extraction wells. U.S. Pat.No. 5,318,116 issued to Vinegar et al., which is incorporated byreference as if fully set forth herein, describe ISTD processes fortreating contaminated subsurface soil with thermal conductive heatingapplied to soil from a radiantly heated casing. The heater elements arecommercial nichrome/magnesium oxide tubular heaters with Inconel 601sheaths operated at temperatures up to about 1250° C. Alternatively,silicon carbide or lanthanum chromate “glow-bar” heater elements, carbonelectrodes, or tungsten/quartz heaters could be used for still highertemperatures. The heater elements may be tied to a support member bybanding straps.

Wells may be arranged in a number of rows and columns. Wells may bestaggered so that the wells are in a triangular pattern. Alternatively,the wells may be aligned in a rectangular pattern, pentagonal pattern,hexagonal pattern or higher order polygonal pattern. In certain wellpattern embodiments, a length between adjacent wells is a fixed distanceso that a polygonal well pattern is a regular well pattern, such as anequilateral triangle well pattern or a square well pattern. In otherwell pattern embodiments, spacing of the wells may result in non-regularpolygonal well patterns. A spacing distance between two adjacent wellsmay range from about 1 m to about 13 m or more. A typical spacingdistance may be from about 2 m to about 4 m.

Wells inserted into soil may be extraction wells, injection wells and/ortest wells. An extraction well may be used to remove off-gas from thesoil. The extraction well may include a perforated casing that allowsoff-gas to pass from the soil into the extraction well. The perforationsin the casing may be, but are not limited to, holes and/or slots. Theperforations may be screened. The casing may have several perforatedzones at different positions along a length of the casing. When thecasing is inserted into the soil, the perforated zones may be locatedadjacent to contaminated layers of soil. The areas adjacent toperforated sections of a casing may be packed with gravel or sand. Thecasing may be sealed to the soil adjacent to non-producing layers toinhibit migration of contaminants into uncontaminated soil. Anextraction well may include a heating element that allows heat to betransferred to soil adjacent to the well.

In some soil remediation processes, a fluid may be introduced into thesoil. The fluid may be, but is not limited to, a heat source such assteam, a solvent, a chemical reactant such as an oxidant, or abiological treatment carrier. A fluid, which may be a liquid or gas, maybe introduced into the soil through an injection well. The injectionwell may include a perforated casing. The injection well may be similarto an extraction well except that fluid is inserted into the soilthrough perforations in the well casing instead of being removed fromthe soil through perforations in the well casing.

A well may also be a test well. A test well may be used as a gassampling well to determine location and concentration of contaminantswithin the soil. A test well may be used as a logging observation well.A test well may be an uncased opening, a cased opening, a perforatedcasing, or combination cased and uncased opening.

A wellbore for an extraction well, injection well, or test well may beformed by angering a hole into the soil. Cuttings made during theformation of the augered hole may have to be treated separately from theremaining soil. Alternatively, a wellbore for an extraction well,injection well, or test well may be formed by driving and/or vibrating acasing or insertion conduit into the soil. U.S. Pat. No. 3,684,037issued to Bodine and U.S. Pat. No. 6,039,508 issued to White describedevices for sonically drilling wells. Both of these patents areincorporated by reference as if fully set forth herein.

A covering may be placed over a treatment area. The covering may inhibitfluid loss from the soil to the atmosphere, heat loss to the atmosphere,and fluid entry into the soil. Heat and vacuum may be applied to thecover. The heat may inhibit condensation of contaminants on the coveringand in soil adjacent to the covering. The vacuum may remove vaporizedcontaminants from the soil adjacent to a soil/air interface to anoff-gas treatment system.

An off-gas collection piping system may be connected to vapor extractionwells of a heating and vapor extraction system. The off-gas collectionpiping system may also be connected to an off-gas treatment system sothat off-gas removed from the soil may be transported to the treatmentsystem. Typical off-gas collection piping systems are made of metalpipe. The off-gas collection piping may be un-heated piping thatconducts off-gas and condensate to the treatment facility.Alternatively, the off-gas collection piping may be heated piping thatinhibits condensation of off-gas within the collection piping. The useof metal pipe may make a cost of a collection system expensive.Installation of a metal pipe collection system may be labor and timeintensive. In some embodiments, off-gas collection piping may be or mayinclude polymer piping and/or flexible hose.

Off-gas within a collection piping system may be transported to anoff-gas treatment system. The treatment system may include a vacuumsystem that draws off-gas from the soil. The treatment system may alsoremove contamination within the off-gas to acceptable levels. Thetreatment facility may include a reactor system, such as a thermaloxidizer, to eliminate contaminants or to reduce contaminants within theoff-gas to acceptable levels. Alternatively, the treatment system mayuse a mass transfer system, such as passing the off-gas throughactivated carbon beds, to eliminate contaminants or to reducecontaminants within the off-gas to acceptable levels. A combination of areactor system and a mass transfer system may also be used to eliminatecontaminants or to reduce contaminants within the off-gas to acceptablelevels.

Instrumentation and power control systems may be used to monitor andcontrol the heating rate of a soil remediation system. Theinstrumentation and power control system may also be used to monitor thevacuum applied to the soil and to control of the operation of theoff-gas treatment system. Electrical heaters may require controllersthat inhibit the heaters from overheating. The type of controller may bedependent on the type of electricity used to power the heaters. Forexample, a silicon controlled rectifier may be used to control powerapplied to a heater that uses a direct current power source, and a zerocrossover electrical heater firing controller may be used to controlpower applied to a heater that uses an alternating current power source.In some embodiments, the use of controllers may not be necessary.

A barrier may be placed around a region of soil that is to be treated.The barrier may include metal plates that are driven into the soilaround a perimeter of a contaminated soil region. A top cover for thesoil remediation system may be sealed to the barrier. The barrier maylimit the amount of air and water drawn into the treatment area from thesurroundings. The barrier may also inhibit potential spreading ofcontamination from the contaminated region to adjacent areas and/or theatmosphere.

SUMMARY

In a soil remediation embodiment, a heated first site may be used to atleast partially destroy contaminants in vapors generated fromcontaminated soil at a second site. Vapors from the contaminated soil atthe second site may be allowed to enter the heated first site.Contaminants in the vapors from the second site transferred to the firstsite may be at least partially destroyed by heat at the first site. Inan embodiment, vapors from more than one site may be transferred to asite of heated, substantially uncontaminated soil. At least partiallydestroying contaminants from a second site at a heated first site maymake efficient use of the energy needed to heat the first site.Destroying contaminants in a site may reduce or eliminate equipmentneeded to process vapors removed from soil during remediation. Forexample, destroying contaminants in a heated site may eliminate a needfor a thermal oxidizer. Eliminating the need for a thermal oxidizer mayadvantageously remove the most expensive, or one of the most expensive,pieces of equipment to obtain, transport, and/or operate.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention will become apparent upon reading thefollowing detailed description and upon reference to the accompanyingdrawings in which:

FIG. 1 shows a schematic plan view representation of an embodiment of asoil remediation system.

FIG. 2 shows a schematic plan view representation of an embodiment of asoil remediation system.

FIG. 3 shows a schematic view of an embodiment of a treatment system forprocessing off-gas removed from soil.

FIG. 4 depicts a side representation of an embodiment of an extractionwell inserted into soil.

FIG. 5 depicts a front representation of an embodiment of an extractionwell inserted into soil.

FIG. 6 depicts a representation of an embodiment of an extraction wellwith a radiant heater element.

FIG. 7 depicts a representation of an embodiment of a heat injectionwell that conductively heats soil.

FIG. 8 depicts a representation of an embodiment of a heat injectionwell positioned within a casing.

FIG. 9 depicts a representation of an embodiment of a heat injectionwell that radiatively heats soil.

FIG. 10 depicts a representation of an embodiment of a heater elementpositioned within a trench.

FIG. 11 is a perspective view of a portion of a heater element that hasa varying cross-sectional area.

FIG. 12 is a perspective view of an embodiment of a heater element.

FIG. 13 depicts a schematic representation of a layout plan for heaterelements placed in trenches.

FIG. 14 depicts a vertical cross-sectional representation along a widthof a pile of soil at a remediation site.

FIG. 15 depicts a vertical cross-sectional representation along a widthof a pile of soil contained by a retaining structure.

FIG. 16 depicts contaminated soil in a remediation pit.

FIG. 17 depicts contaminated soil in a tank.

FIG. 18 depicts a heated riser for removing contaminants fromcontaminated soil.

FIG. 19 depicts an embodiment of a remediation site including twotreatment sites.

FIG. 20 depicts an embodiment of simultaneous remediation ofcontaminated soil from more than one location.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Thedrawings may not be to scale. It should be understood, however, that thedrawings and detailed description thereto are not intended to limit theinvention to the particular form disclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the present invention as definedby the appended claims.

DETAILED DESCRIPTION

A soil remediation system may remove or reduce contaminants within aselected soil region. FIGS. 1 and 2 show schematic representations ofembodiments of soil remediation systems 30. Soil remediation system 30depicted in FIG. 1 may include one or more extraction wells 32 withinsoil 34. Soil remediation system 30 may optionally include one or moreheat injection wells 36, one or more fluid injection wells 38, and oneor more test wells 40. Fluid injection wells 38 and/or test wells 40 maybe located inside or outside of a pattern of extraction wells 32 andheat injection wells 36. Extraction wells 32, heat injection wells 36,fluid injection wells 38, and/or test wells 40 may include well casings.Portions of the well casings may be perforated to allow fluid to passinto or out of the well casings. Alternatively, extraction wells 32,heat injection wells 36, fluid injection wells 38, and/or test wells 40may include a cased portion and an uncased portion. The uncased portionmay be adjacent to contaminated soil.

In some embodiments, soil remediation system 30 may be used for in situsoil remediation. In other embodiments, soil remediation system 30 maybe used for ex situ soil remediation. In some soil remediation systems,extraction wells 32, heat injection wells 36, fluid injection wells 38,and/or test wells 40 may be placed substantially vertically in soil 34.In some soil remediation system embodiments, extraction wells 32, heatinjection wells 36, fluid injection wells 38, and/or test wells 40 maybe place substantially horizontally in soil 34.

In addition to extraction wells 32, heat injection wells 36, fluidinjection wells 38, and/or test wells 40, soil remediation system 30 mayinclude ground cover 42, treatment facility 44, vapor collection system46, control system 48, and/or pumping units 50. Ground cover 42 may beplaced over extraction wells 32, heat injection wells 36, fluidinjection wells 38, and/or test wells 40 to inhibit heat loss andcontaminant vapor loss to the atmosphere. Ground cover 42 may alsoinhibit excess air from being drawn into soil 34. Ground cover 42 mayinclude a layer of thermal insulation. Ground cover 42 may include alayer that is impermeable to contaminant vapor and/or air. Theimpermeable layer may include, but is not limited to, metal sheetingand/or concrete. Wells positioned substantially vertically in the soilmay be welded or otherwise sealed to the metal sheet. Wells positionedsubstantially horizontally in the soil may be positioned beneath themetal sheet. Vertical barriers may be inserted into the soil around aperimeter of the metal sheet to form an end barrier. Thermal insulationmay typically be placed above the impermeable barrier. The thermalinsulation may include, but is not limited to, mineral or cotton wool,glass wool or fiberglass, polystyrene foam, or aluminized mylar.

Optional surface heaters may be placed on or below ground cover 42. Thesurface heaters may inhibit contamination from condensing on groundcover 42 and flowing back into soil 34. The surface heaters aretypically electrically powered heaters.

A gas and water barrier of ground cover 42 may be placed over theremediation site. The gas and water barrier may be plastic sheeting. Anyopenings or connections to equipment may be sealed with a silicone orother type of sealant.

Ground cover 42 may not be needed if the contamination is so deep withinsoil 34 that heating the soil and removing off-gas from the soil willhave negligible effect at ground surface 52 of the soil. If a cover isnot utilized, a vacuum source may be needed to draw a vacuum aroundwellheads 54 of heat injection wells and/or extraction wells to inhibitrelease of vapor to the atmosphere from the wells. Wellhead 54 isequipment and/or structure attached to an opening of a well.

Treatment facility 44 may include vacuum system 56 that draws an off-gasstream from soil 34 through extraction wells 32. If the soil remediationsystem includes surface heaters, vacuum system 56 may be configured todraw vacuum at ground surface 52 as well as in extraction wells 32. Thevacuum drawn in extraction wells 32 may be stronger than the vacuumdrawn at surface 52. Treatment facility 44 may also include contaminanttreatment system 58 for treating contaminants within the off-gas.Contaminant treatment system 58 may eliminate contaminants from theoff-gas stream, reduce contaminants to acceptable levels, and/orconcentrate contaminants for off-site transport. Contaminant treatmentsystem 58 may include, but is not limited to, separators, condensers,reactor systems, mass transfer systems, and chemical storage vessels.

FIG. 3 shows an embodiment of treatment system 58. Off-gas from vaporcollection system 46 may pass into separator 60. Separator 60 mayseparate the off-gas into a liquid stream and a vapor stream. Vacuumsystem 56 that is in-line with the vapor stream may provide the vacuumto soil 34 to remove off-gas from the soil. Vacuum system 56 should becapable of pulling a vacuum appropriate for the particular combinationof soil permeability and extraction wells within a treatment system.Vacuum system 56 may be able to pull a vacuum in the range of 0.01atmospheres to slightly less than 1 atmosphere. The vacuum system may bea water sealed pump.

Liquid and vapor streams may be processed by treatment system 58 toreduce contaminants within the streams to acceptable levels. Monitoringequipment may determine the quantity of contaminants in processedstreams. The monitoring equipment may sound an alarm and/or beginrecirculation of output streams from treatment system 58 back to thebeginning of the treatment system if too much contamination is detectedin the output streams.

A liquid stream may be separated by second separator 62 into anon-aqueous stream and an aqueous stream. In an embodiment, secondseparator 62 and separator 60 may be a single unit. The non-aqueousstream may include oils and other non-aqueous material. The non-aqueousstream may be very small compared to the aqueous stream. The non-aqueousstream may be sent to treatment unit 64. Treatment unit 64 may place thenon-aqueous stream in storage containers, such as waste barrels. Thecontainers may be transported off-site for disposal. Alternatively,treatment unit 64 may be an oxidization system, thermal system, or otherreaction system that eliminates or reduces to acceptable levelscontaminants within the non-aqueous stream.

Pump 66 may be used to move the aqueous stream. Pump 66 may transportthe aqueous stream through activated carbon bed 68. Activated carbon bed68 removes contaminants from the aqueous stream. The remaining aqueousstream may then be discharged. For example, after the aqueous stream haspassed through activated carbon bed 68, the aqueous stream may be sentto sanitary sewer 70.

The vapor stream from separator 60 may pass through treatment unit 72.Treatment unit 72 may be a mass transfer system such as activated carbonbed, a reactor system such as a thermal oxidizer, or a combinationthereof. Blower 74 may draw the vapor stream through treatment unit 72and vent the remaining vapor to the atmosphere.

In some embodiments of treatment systems 58, the treatment systems maynot include thermal oxidizers to eliminate or reduce contaminants withinoff-gas to acceptable levels. Carbon beds, concentrators, or non-thermalreactor systems may be used instead of thermal oxidizers. Replacement ofthermal oxidizers with other equipment that eliminates or reducescontaminants may lower capital costs, transportation costs, and/oroperation costs of a soil remediation system. A thermal oxidizer may bevery expensive to obtain and to transport to treatment locations. Also,thermal oxidizers may require on-site monitoring by operationalpersonnel to ensure that the thermal oxidizer is functioning properly.Removing a thermal oxidizer from a soil remediation process maysignificantly improve economics of the process.

As shown in FIG. 1, vapor collection system 46 may include a pipingsystem that transports off-gas removed from soil 34 to treatmentfacility 44. The piping system may be coupled to vacuum system 56 and toextraction wells 32. In an embodiment, the piping may be un-heatedpiping and/or un-insulated piping. Off-gas produced from the soil mayinitially rise vertically and then travel downward to the treatmentfacility. The initial rise and subsequent downward travel may allow anycondensed off-gas to pass to a liquid trap or to a separator of thetreatment system without blocking lines of the collection system. Inalternative embodiments, the piping may be thermally insulated and/orheated. Insulated and heated piping inhibits condensation of off-gaswithin the piping. Having a non-insulated and non-heated collectionsystem may greatly reduce cost, installation time, and complexity of asoil remediation system.

Control system 48 may be a computer control system. Control system 48may monitor and control the operation of treatment facility 44. If vaporcollection system 46 includes heated piping, control system 48 maycontrol power applied to line tracers that heat the piping. Ifextraction wells 32 or heat injection wells 36 include non-selfregulating heater elements, the control system may control power appliedto heater elements of the extraction wells.

Heat may be applied to soil 34 during a soil remediation process. Heatmay be applied to soil from heat injection wells 36, from extractionwells 32, and/or from other heat sources. Heat may be applied to soil 34from electrical resistance heater elements positioned within theextraction wells. Power may be supplied from power source 76 toextraction wells 32 and heat injection wells 36 through cables 78. Powersource 76 may be a transformer or transformers that are coupled to highvoltage power lines. In some embodiments of soil remediation systems,heat may be applied to the soil by other heat sources in addition to orin lieu of heat being applied from electrical resistance heaterelements. Heat may be applied to soil, but is not limited to beingapplied to soil, by combustors, by transfer of heat with a heat transferfluid, by radio frequency or microwave heating, and/or by soilresistivity heating.

Extraction wells 32 depicted in FIG. 1 are heater/vapor extractionwells. Heat generated by electrical resistance heaters within extractionwells 32 apply heat to soil and to fluids being produced. Heat generatedby heater elements within extraction wells 32 flows countercurrent tomass flow of off-gas within soil 34. The countercurrent flow of heat andmass may allow the off-gas to be exposed to high temperatures adjacentto and in extraction wells 32. The high temperatures may destroy asignificant portion of contaminants within the off-gas. In otherembodiments of soil remediation systems, some of the extraction wells,or all of the extraction wells, may not include heater elements thatheat the soil.

In some soil remediation system embodiments, heat may be applied to thesoil only from heater/vapor extraction wells. In other embodiments, suchas the embodiment depicted in FIG. 1, only selected wells within thesoil are heater/vapor extraction wells. Using only some heater/vaporextraction wells may significantly reduce cost of the soil remediationsystem. Heater/vapor extraction wells are typically more expensive thanheater wells. Installation and connection time for heater/vaporextraction wells is typically more expensive and longer for heater/vaporextraction wells than for heater wells. A vapor collection system mayneed to be much more extensive, and thus more expensive, for a soilremediation system that uses exclusively heater/vapor extraction wells.

In some embodiments of soil remediation systems, heat may be provided tosoil 34 from heat injection wells 36 and/or from extraction wells 32.Heat injection wells 36 are not coupled to vacuum system 56.Superposition of heat from heater elements of heat injection wells 36and/or extraction wells 32 may allow a temperature of soil 34 within atreatment area to rise to a desired temperature that will result inremediation of the soil. Extraction wells 32 may remove off-gas fromsoil 34. The off-gas may include contaminants and/or reaction productsof contaminants that were within soil 34.

Extraction wells 32 and heat injection wells 36 may be placed in desiredpatterns within soil 34 that is to be remediated. The patterns ofextraction wells 32 and heat injection wells 36 may be, but are notlimited to, triangular patterns (as shown for extraction wells 32),rectangular patterns, pentagonal patterns, hexagonal patterns (as shownfor heat injection wells 36), or higher order polygon patterns. Anactual soil remediation system will typically have many more wellswithin a treatment area than depicted in the schematic representation ofFIG. 1. The well patterns may be regular patterns to promote uniformheating and off-gas removal throughout a treatment area. For example,well patterns may be equilateral-triangle patterns or square-wellpatterns. Extraction wells 32 and heat injection wells 36 of thepatterns may be substantially uniformly placed throughout a treatmentarea. Some of extraction wells 32 and/or heat injection wells 36 may beoffset from the regular patterns to avoid obstacles in or on the soil.Obstacles may include, but are not limited to, structures; impermeable,uncontaminated regions amid contaminated soil; property lines; andunderground or above ground pipes or electrical lines. Spacing betweencenters of wells may range from about 1 m to 13 m or more. Spacing maybe determined based on time allowable for remediation, soil properties,type of soil contamination and other factors. A close well spacing mayrequire less heating time to raise soil temperature to a desiredtemperature, but close well spacings require many more additional wellsto heat the soil than would be required with a larger well spacing.

Some soil remediation systems may include fluid injection wells 38.Fluid injection wells 38 may be used to introduce a fluid into soil 34.The fluid may be, but is not limited to, a reactant, a biological agent,and/or a flooding agent. The fluid may be injected into soil 34 bypumping units 50. Alternatively, vacuum applied to extraction wells 32may draw fluid into soil 34 from fluid injection wells 38.

Some soil remediation systems may include test wells 40. Fluid samplesmay be withdrawn from test wells 40 to allow determination of theprogress of soil remediation at selected locations and at selectedtimes. Monitoring equipment may be positioned in test wells 40 tomonitor temperature, pressure, chemical concentration, or otherproperties during a soil remediation process.

FIG. 2 depicts a representation of soil remediation system 30 that usesonly heater/vapor extraction wells as extraction wells 32. Power source76 that heats the heater elements within extraction wells 32 may be athree phase transformer. For example, power source 76 may be a 112.5 kVAtransformer that has a 480 VAC 3-phase primary and a 3-phase secondary.Each phase may be used to power a group of extraction wells 32 that areelectrically connected in series. If more than three groups ofextraction wells 32 are needed to process a treatment area, sections ofthe area may be sequentially treated, or additional power sources may beused so that the entire treatment area is processed at one time.Extraction wells 32 may be directly coupled to power source 76 withoutthe use of well controllers if the heater elements are made of metalshaving self-regulating temperature properties. The heater elements ofextraction wells 32 and power source 76 are designed to reach a desiredtemperature when connected to the power source. Heater elements may bedesigned to heat to a maximum temperature of about 1250° C. Heaterelements may be designed to have a steady state operating temperature ofabout 900° C. An operating range of heater elements may extend fromambient soil temperature to about 1250° C.

Off-gas drawn from soil 34 by vacuum may pass through hoses 80 andvacuum manifold 82 to a treatment facility 44. Hoses 80 and vacuummanifold 82 may be components of vapor collection system 46. Hoses 80may attach to vacuum casings of extraction well 32 and to vacuummanifold 82. The vacuum casing may extend through covering 42 and mayrise to a height sufficient to allow the remainder of the vaporcollection system 46 to slope downwards to treatment facility 44.Sealant such as welds, silicone rubber sealant, or other types ofsealant may be used to seal casings of extraction wells 32 and otherstructures that pass through covering 42 to the casing. Seals mayinhibit vapor and/or liquid from passing into or out of covering 42.

Hose 80 may be attached to each extraction well casing and to vacuummanifold 82 by solvent glue and/or clamps, or by other attachmentmethods including, but not limited to, threading or flanges. Hoses 80may be formed of high temperature rubber that has an upper workingtemperature limit of about 230° C. Hoses 80 are conduits fortransporting off-gas from extraction wells 32 to vacuum manifold 82.Off-gas passing through hose 80 has a residence time within the hose.Hose 80 may have a sufficient length so that the residence time ofoff-gas within the hose is sufficiently long to allow the off-gas tocool. The off-gas may cool within hoses 80 to a temperature that is ator below an upper working temperature limit of the material that formsvacuum manifold 82.

Vacuum manifold 82 may be formed of plastic piping. The plastic pipingmay be chlorinated polyvinyl chloride (CPVC) piping or other plasticpiping that has a high upper working temperature limit. The upperworking temperature limit of CPVC piping is approximately 90° C. Off-gasmay cool as it flows through vacuum manifold 82. Portions of vacuummanifold 82 located away from extraction wells 32 may be formed ofplastic piping, such as PVC piping, that has a lower working temperaturelimit than CPVC piping.

The use of a collection system including hoses 80 and plastic pipingvacuum manifold 82 may result in lower costs, simplified on-siteconstruction, and lower mobilization costs as compared to a metal pipingcollection system. A collection system including hoses and plasticpiping may not be insulated and/or heated, thus greatly reducing thecost, installation time, and operating cost of the collection system.Hose 80 may be rolled into coils for transportation. Plastic piping maybe purchased locally near the site. Hose 80 and plastic piping areeasily cut to size on-site and are connectable by solvent gluing orother techniques. Also, hose 80 and plastic piping are lightweight anddo not require machinery to lift and position during installation.Unlike some metal piping, hose 80 and the plastic piping may be highlyresistant to corrosion caused by the off-gas. For example, off-gas mayinclude hydrogen chloride, especially if the soil contamination includeschlorinated hydrocarbons. If the hydrogen chloride forms hydrochloricacid with condensed water, the acid may rapidly corrode metal vaporcollection piping. Hose 80 and plastic piping may be highly resistant toHCl corrosion.

FIGS. 4, 5, and 6 depict embodiments of extraction wells 32 that includeheater elements 84. Heater elements 84 may be bare metal without aninsulation coating such as mineral insulation. Using uninsulated, baremetal heater elements may significantly reduce heater cost as comparedto conventional heater elements, such as mineral insulated cables.Heater elements 84 may be placed in soil 34 without being tied to asupport member such as a conduit or a support cable. Eliminating asupport cable or conduit reduces cost, installation time, and laborassociated installing the heater element. An electrical current may bepassed through heater elements 84 to resistively heat the heaterelements.

A vacuum system may remove off-gas from soil 34 through openings 86 invacuum casing 88. FIGS. 4 and 5 depict embodiments of extraction wellsthat conductively heat soil 34. Heater elements 84 shown in FIGS. 4 and5 heat packing material 90 that conducts heat to adjacent soil. Packingmaterial 90 may be sand, gravel, or other fill material that may besubjected to high temperatures. The fill material may include catalyst92. Catalyst 92 may be a metal, metal oxide, or other type of catalystthat enhances pyrolysis and/or oxidation of contaminants that passthrough the packing material. In an embodiment, the catalyst is alumina.

Heater elements that are packed with fill material in the soil maythermally expand towards the surface when heated. Allowance needs to bemade at wellheads to allow for expansion of the heater elements.

FIG. 6 depicts an embodiment of extraction well 32 that includes heaterelements that radiatively heats heater well casing 94. The inner surfaceof heater casing 94 may be blackened, textured, oxidized, or otherwisetreated to increase radiative heat transfer between heater element 84and the heater casing. Heater well casing 94 may radiatively heat vacuumcasing 88. The inner surface of the vacuum casing may be blackened,textured, oxidized, coated, or otherwise treated to increase radiativeheat transfer between the heater casing and the vacuum casing.Alternatively, annular space between the heater casing and the vacuumcasing may be filled with packing material. The packing material mayinclude a catalyst that enhances pyrolysis or oxidation of contaminantsthat pass through the packing material.

Heater well casing 94 may prevent current leakage into soil 34 as mayoccur with heater elements that do not have casings. Some currentleakage may be acceptable because the current leakage may heat water orsoil that is drawing current from the heater elements. If excessivecurrent leak is possible, an external casing may be used to surround theheater element. Heater well casing 94 may be used when the well is to bepositioned in a water saturated zone or in soil that has a high saltcontent or contains brackish water.

Heater elements 84 that radiatively heat heater well casing 94 or soil34 may expand downwards when heated. Heater well casing 94 or theopening in the soil defined by opening wall 96 that the heater elementis placed in should be sufficiently long to accommodate thermalexpansion of heater element 84 and heater well casing 94.

As depicted in FIG. 6, spacers 98 may be placed along a length of heaterelement 84 to prevent the heater element from contacting, orelectrically arcing, to an adjacent conduit such as heater well casing94. Spacers 98 may also prevent leg 100 of heater element 84 that isbent into “U” shapes from contacting, or electrically arcing, to anadjacent leg of the heater element. Spacers 98 may be made of ceramicinsulators. For example, spacers may be made of high alumina ceramicinsulation material. Spacers 98 may be obtained from Cooper Industries(Houston, Tex.). Spacers 98 may slide onto heater elements 84. A weldbead may be formed beneath a place where spacer 98 is to be located sothat the spacer cannot pass the weld bead. In an embodiment of a heaterelement that is vertically positioned in a well, as depicted in FIG. 6,spacers 98 may be positioned about every ⅓ m to about every ½ m along alength of the heater element. Shorter or longer spacings may be used toaccommodate particular heater elements and system requirements.Horizontally oriented heater elements placed within heater well casingsmay require closer spacings to inhibit sagging of the heater elementwhen the heater element is heated. Spacers 98 may also be positionedbetween vacuum casing 88 and/or soil and heater element 84 thatconductively heats fill material 90, as depicted in FIG. 5.

FIGS. 7, 8, and 9 depict embodiments of heat injection wells 36. Heatinjection wells 36 include heater elements 84. An electrical current maybe passed through the heater elements 84 to resistively heat the heaterelements. FIG. 7 depicts an embodiment of a heat injection well 36having heater element 84 that conductively heats soil 34. FIG. 8 depictsa heat injection well embodiment having heater element 84 that isenclosed in heater casing 94. In certain embodiments, heater casing 94may be packed with fill material. In other embodiments, the heatercasing may radiatively heat the heater casing. FIG. 9 depicts a heatinjection well embodiment having heater element 84 that radiativelyheats adjacent soil 34.

FIG. 10 depicts a representation of an embodiment of heater element 84positioned within a trench near to ground surface 52. Heater element 84is shown below contamination interface 102 in uncontaminated soil 104.In other embodiments, heater element 84 may be positioned withincontaminated soil 106, or at or near contamination interface 102. Heaterelement 84 is shown as having 90° angles to the surface. In practice,ends of the trench may taper towards the surface, and ends of heaterelement 84 may be positioned on the tapering ends of the trench.

Vacuum drawn by a treatment facility may be applied near soil surface52. Permeable mat 108 may be placed on top of soil surface 52.Impermeable barrier 110 and thermal barrier 112 may be placed on top ofmat 108. Mat 108 may serve as a conduit for flow beneath impermeablebarrier 110. In an embodiment, mat 108 may be a thin layer of highpermeability sand or other granular material. Mat 108 may includecatalyst material that enhances thermal degradation of contaminants thatpass through the mat. Mat 108 may allow off-gas to flow out of soil 34to vacuum manifold 82 positioned above the mat. The off-gas may floweven when the vacuum draws impermeable barrier 110 against mat 108 andcompresses the mat. Thermal barrier 112 may inhibit heat transfer.Alternatively, vapor extraction wells may be inserted into the soilthroughout the treatment site to draw off-gas from the soil.

As shown in FIGS. 4–10, heater elements 84 may include heater sections114, transition sections 116, and pins 118. Some heater elements 84 maynot include transition sections between heater sections 114 and pins118. All or substantially all of heater section 114 of heater element 84may be bare metal. “Bare metal” as used herein refers to a metal thatdoes not include a layer of electrical insulation, such as mineralinsulation, that is designed to provide electrical insulation for heatersection 114 during use. Bare metal may encompass a metal that includes acorrosion inhibiter such as a naturally occurring oxidation layer, anapplied oxidation layer, and/or a film. Bare metal includes metal withpolymeric or other types of electrical insulation that cannot retainelectrical insulating properties at typical operating temperatures ofheater section 114 of heater element 84. Such material may be placed onthe metal and may be designed to be destroyed during a soil remediationprocess. Weld material and/or connector sections of heater sections 114may include electrical insulation material without changing the natureof the heater element into an insulated heater element. Insulatedsections of heater section 114 of heater element 84 may be less than 5%,1%, 0.5%, or 0.1% of a length of the heater section. Bare metal heaterelements 84 significantly reduce production cost and increaseavailability of heater elements as compared to heater elements thatinclude insulated heater sections 114.

In certain embodiments of heater elements 84, portions of transitionsections 116 and/or portions of pins 118 may be electrically insulated.In other embodiments of heater elements 84, all of the heater elementmay be bare metal.

Heater elements 84 depicted in FIGS. 4–10 are positioned substantiallyvertically or horizontally. Heater elements may be positioned at anydesired orientation from 0° (horizontal) to 90° (vertical) relative toground surface. For example, in a soil remediation system embodiment,heater elements may be oriented at about 45° to remediated soil adjacentto a geological layer that slopes at about 45°. The orientation may bechosen to result in relatively low cost, quick, and efficient soilremediation.

Heater sections 114 of heater elements 84 may be formed of metals thatare capable of sustained use at high operating temperatures. Portions ofheater element 84 may operate from ambient soil temperatures tosustained temperatures of over 1000° C. In certain heater elementembodiments, such as the heater elements depicted in FIGS. 4, 5, 7, 9,and 10, portions, or all, of heater elements 84 may be exposed tooff-gas during soil remediation. Such heater elements 84 may need to bemade of corrosion resistant metal. The resistance of heater sections 114to corrosion may be very important. High temperature and high amperageat which heater sections 114 operate may promote corrosion of heatersections 114. Corrosion may decrease cross-sectional areas of heatersections 114 at certain locations along lengths of the heater sections.Decreased cross-sectional areas of heater sections 114 may cause theheater sections to overheat and fail.

Heater sections 114 may be formed of stainless steel. The stainlesssteel may be, but is not limited to, type 304 stainless steel, type 309stainless steel, type 310 stainless steel, or type 316 stainless steel.Heater sections 114 may also be formed of other metals including, butnot limited to, Nichrome®, Incoloy®, Hastelloy®, or Monel®. For example,heater section 114 may be made of Nichrome® 80 or Incoloy® 800.

A specific metal used to form heater section 114 of heater element 84may be chosen based on cost, temperature of the soil remediationprocess, electrical properties of the metal, physical properties of themetal, and chemical resistance properties of the metal. For example, 310stainless steel is a high temperature stainless steel that may dissipateabout 20% more power than 304 stainless steel of equivalent dimensions.The corrosion resistance of 310 stainless steel is better than thecorrosion resistance of 304 stainless steel. The upper workingtemperature limit of 310 stainless steel is about 160° C. higher thanthe upper working temperature limit of 304 stainless steel.

The extra temperature range of 310 stainless steel may be used todissipate extra heat into soil and shorten remediation time. The extratemperature range may be used as a safety margin to insure againstoverheating the heater element. A cost of 310 stainless steel may beabout 25% more than a cost of 304 stainless steel. At a design stage ofa soil remediation process, a determination may be made of whether thebetter characteristics of 310 stainless steel justify the extra cost ofthe 310 stainless steel above the cost of 304 stainless steel. Similarcomparisons may be made for other metals as well.

Heater sections 114 of heater elements 84 may be formed to have selectedsections that heat to higher or lower temperatures than adjacentsections of heater elements. Portions of heater element 84 that areconfigured to heat to higher temperatures than adjacent portions may bepositioned adjacent to interfaces 102 between contaminated soil 106 anduncontaminated soil 104. The extra temperature produced in the hightemperature portions may help to counter heat loss due to end effects ofheater section 114. High temperature portions may dissipate greater than5%, 15%, 25%, or 30% more heat than adjacent portions of the heatersection. FIG. 11 shows a portion of heater element 84 having a hightemperature portion that is reduced cross-sectional area portion 120positioned adjacent to larger cross-sectional area portions 122. Metalmay be removed from a portion of heater section 114 to form a hightemperature portion of heater section 114. Alternatively, the portionsof a heater section that are to be heated to higher temperatures thanadjacent areas may be portions of a different metal that is moreelectrically resistive than the metal of the adjacent sections. The moreresistive metal may have a larger, same, or smaller cross-sectional areathan adjacent portions of the heater section. Thermally and electricallyconductive weld material may be used to couple portions 120, 122together. Care may be taken to ensure that ends of the different metalsabut and that a large amount of weld material couples the differentmetal portions together. Abutting metal portions and a large amount ofweld material may ensure that failure due to arcing and/or corrosiondoes not occur at junctions between the metals during use.

Portions of heater sections 114 may heat to lower temperatures thansurrounding portions. Such portions may be positioned adjacent to soillayers or obstacles that do not need to be heated to high temperatures.For example, a reduced heating section may be designed to resideadjacent to an impermeable, uncontaminated soil layer that is betweentwo contaminated soil layers. A low heating section may be formed of aheating section having increased cross-sectional area as compared toadjacent areas. Alternatively, a low heating section may be formed of aless electrically resistive metal welded between two adjacent portionsof heater section. Care may be taken to ensure that ends of thedifferent metals abut and that a large amount of weld material couplesthe different metal portions together. Thermally and electricallyconductive weld material may be used to couple the portions together.Abutting metal portions and a large amount of weld material may ensurethat failure due to arcing and/or corrosion does not occur at junctionsbetween the portions during use.

As shown in FIG. 10, transition sections 116 of heater element 84 may bewelded to each end of heater section 114 of the heater element. Pins 118may be welded to transition sections 116. Transition section 116 mayreduce a temperature of heater element 84 so that the temperature at andadjacent to pin 118 is sufficiently cool to allow use of insulatedconnector cable 78 (depicted in FIG. 4) to couple pin 118 to powersource 76. Transition section 116 may be made of the same material asheater section 114, but the transition section may have greatercross-sectional area. Alternatively, the transition section may be madeof a material having less electrical resistance than the heater section.The two sections may be welded together.

FIG. 12 depicts an embodiment of heater element 84 that may be used toradiatively heat soil. Heater element 84 includes welds 124 betweentransition section 116 and heater section 114. Thermally andelectrically conductive weld material may be used to couple sections114, 116 together. Abutting metal sections and a large amount of weldmaterial may ensure that failure due to arcing and/or corrosion does notoccur at a junction between the sections during use.

Pins 118 may be nickel pins. In an embodiment, such as the embodimentdepicted in FIG. 4, pins 118 extend through ground cover 42 when heaterelement 84 is inserted into the soil 34. Connection 126 may electricallycouple the pin to cable 78. Connection 126 may be a mechanical Kerneylug, epoxy canister, or other type of electrical connector. Cable 78 maybe electrically coupled to power source 76. Cable 78 may be anelectrically insulated cable. Transition section 116 and cold pin 118may allow heater element 84, soil 34, and/or cover 42 to be cool enoughto inhibit thermal degradation of the cable insulation during use.

In certain embodiments of heater elements, long sections of relativelylow resistance metal may be attached to heater sections to form longheated sections that generate temperatures sufficient to inhibitcondensation of vapor on or adjacent to the heater element. The lowresistance metal may be, but is not limited to, nickel or alloys ofnickel and copper such as Alloy 30. The long heated sections may beneeded for deep soil contamination that does not come close to theground surface.

Power source 76 (depicted in FIG. 1) for a soil remediation system mayprovide a substantially constant voltage to heater elements of the soilremediation system. Power source 76 may be electrical power from a powerline that passes through a transformer. Output from the transformer maybe coupled to a number of heater wells by parallel and/or seriesconnections to provide an appropriate electrical circuit that will heatsoil to a desired temperature.

Heater section 114 of heater element 84 may have a large cross-sectionalarea as compared to conventional radiant heater elements. The largecross-sectional area may allow heater element 84 to have a smallelectrical resistance as compared to a conventional heater of equivalentlength. The small electrical resistance may allow heater element 84 tobe long. A heater element may be over 10 m, 50 m, or 100 m long, 300 m,500 m or 600 m long. The small electrical resistance may also allowseveral heater elements to be electrically connected in series. Theability to connect several heater elements 84 in series may greatlysimplify wiring requirements of a soil remediation system. For heaterelements that conductively heat adjacent material, the largecross-sectional area of the heater section may mean that there will be alarge contact area between the heater section and adjacent material. Forheater elements that radiatively heat adjacent material, the largecross-sectional area of the heater may mean that the heater section hasa large surface area that will radiate heat to a casing wall or to soil.Also, the large cross-sectional areas of heater elements may allow theheater elements to be placed in the soil without being attached to asupport structure. In an embodiment of a radiative heater element, theheater element is made of 304 stainless steel rod stock having adiameter of about 1 cm.

Radiative heater elements that are suspended within a well casing mayhave telescoping sections of different alloys and/or differentcross-sectional areas to produce long heater elements. A first sectionmay be made of a material that has a high creep resistance at operatingtemperatures of the heater element. The first section may be relativelythick or have a relatively large effective diameter. Many high strength,high creep resistance materials, such as Inconel 617 and HR 120, havehigher electrical resistances than stainless steels that may be used toform primary heater sections of the heater element. Higher resistancematerial allows the high strength and creep resistant sections (one oneach leg of a “U” shaped heater element) to heat to high temperatureseven though the sections have large cross-sectional areas. A secondsection may be made of a less expensive metal that is welded to thefirst metal. The second section may have a smaller thickness oreffective diameter than the first section. Additional sections may bewelded to the strip to form a heater element having a desired length.The diameters of the various metals, taking into consideration theresistivity of the metals, may be adjusted to produce a long heaterelement that dissipates substantially the same amount of energy per unitlength along substantially the entire length of the heater. Metals usedto form the sections may include, but are not limited to Inconel 617, HR120, 316 stainless steel, 310 stainless steel, and 304 stainless steel.In an embodiment of a long, radiative, suspended heater element, a leadin section of about 30 m is made of 316 stainless steel and is used tosuspend the heater element from a wellhead. The lead in sectionfunctions as a heater section of the heating element. A second heatersection may be formed of a narrower cross-sectional area of 304stainless steel (up to about 25% less cross-sectional area to dissipatethe same amount of heat as the lead in section). The second heatersection in the particular embodiment is 160 m in length, resulting in a“U” shaped heater element having a 110 m (30 m+80 m) long heatingsection with a total heater section length of 220 m. A portion of thesecond heater section near a 180° bend (or hairpin turn) in the heaterelement may have a further reduced cross-sectional area or a differentalloy metal to dissipate more heat than adjacent heater elementsections.

In certain embodiments of radiative heater elements, a support sectionof a radiative heater element may have a cross-sectional area thattapers to a substantially constant cross-sectional area. A supportsection may be made of the same material or a different material thanother portions of a heater element. The support section may be atransition section of a heater element that does not need to rise tohigh operating temperatures. The support section may be a portion ofheater section that will rise to high operating temperatures during use.

For a heater element that conductively heats adjacent material, a heatersection may have a substantially rectangular cross-sectional area. Forexample, an embodiment of a heater section 26 has a 25 millimeter (mm)by 3 mm rectangular cross section and a length of about 6 m. Thedimensions of a heater section may be chosen so that the heater sectionproduces and dissipates a desired amount of heat when inserted into soiland when coupled to a power source. Cross-sectional shapes other thanrectangular shapes may also be used. The cross-sectional shapes may be,but are not limited to, ellipsoidal, circular, arcuate, triangular,rectangular, pentagonal, hexagonal, or higher order polygon shaped.Heater elements that transfer heat by radiation may typically have asubstantially circular cross-sectional area, but other cross-sectionalareas, such as the cross-sectional areas referred to above, may also beused.

Heater elements may be positioned within the soil in a variety of ways.Some heater elements 84 may be directly placed within the soil, such asthe embodiment of a heater element depicted in FIG. 7. Other heaterelement embodiments may be separated from the soil by packing material90, such as is depicted in the embodiment of FIG. 4. Other heaterelements may be placed in heater element casings 94, such as the heaterelement depicted in FIG. 6. Heater element casing 94 may be placed orpacked in the soil, or the heater casing may be placed in vacuum casing88 that is placed or packed in the soil. Placing heater element 84 inheater element casing 94 may allow the heater element to be made of arelatively inexpensive, non-corrosion resistant material, becauseoff-gas will not come into direct contact with the heater element.Heater element casing 94 may be made of a material that has sufficientcorrosion resistance to resist breakthrough corrosion during theestimated time needed to complete soil remediation.

Heater element 84 in FIG. 4 may be driven directly into the soil. Adrive rod may be positioned at the center of heater element 84. Thedrive rod may then be pounded into soil 34. When heater element 84 isinserted to a desired depth, the drive rod may be withdrawn. The driverod does not need to be a continuous rod. The drive rod may be made ofthreaded sections that are assembled together as the drive rod ispounded deeper into soil 34. A geoprobe or a cone penetrometer rig maybe used to drive heater element 84 into soil 34. Also, a sonic rig maybe used to vibrate heater element 84 to a desired depth. The sonic rigmay include an eccentric cam that vibrates heater element 84 and a driverod to a desired soil depth. Driving or vibrating heater element 84 intosoil 34 may not produce cuttings as are produced when an augered openingis formed in the soil. Driving or vibrating heater element 84 mayeliminate problems associated with disposing of cuttings produced duringthe formation of an augered hole. Avoidance of the production ofcuttings may be particularly advantageous at extremely toxic orradioactive sites. Also, driving or vibrating heater element 84 intosoil 34 may advantageously place a portion of heater element 84 indirect contact with the soil to be heated.

For heater elements placed in openings or well casings, heater elements84 may be formed in “U” shapes so that ends of both legs 100 of theheater element are accessible at ground surface 52. Accessibility ofboth legs 100 allows many heater elements 84 to be easily andefficiently coupled together electrically. Spacers may be positioned atdesired locations along a length of the heater element. The heaterelement may be lowered into the opening or casing. If fill material isto be used to pack the casing, as depicted in FIG. 4, fill material 90may be placed adjacent to heater element 84. To place the fill material90, a fill pipe, such as a polyvinyl chloride pipe, may be insertedbetween legs 100 of “U”-shaped heater element 84. If fill material is tobe placed between legs 100 of the heater element and soil 34, tubessuspended by wire may be lowered down the legs of the heater element.The tubes may be raised as fill material 90 is placed in the opening.The tubes may properly position each leg of heater element 84. Incertain embodiments, the fill pipe may press the heater element againstthe soil. Fill material 90 may be inserted through the fill pipe whileraising the fill pipe out of soil 34. Fill material 90 may plug spacesbetween heater element 84 and soil 34. Fill material 90 may include sandand/or gravel. Fill material 90 may also include catalyst 92, such asaluminum oxide. Catalyst 92 may be a component of fill material for bothextraction wells 32 and heat injection wells 36. Fill material 90 may beheated to remove moisture before being inserted through the fill pipe.Fill material 90 may be built up in a mound at soil surface 52 topromote water runoff away from heater element 84.

Thermocouple well 128 may be positioned in fill material 90 between legs100 of U-shaped heater element 84. A thermocouple placed in thermocouplewell 128 may be used to measure the temperature between legs 100 ofheater element 84 during soil remediation. The thermocouple may belowered or raised to determine temperatures at selected depths.Alternatively, the thermocouple may be fixed within the thermocouplewell. In an embodiment depicted in FIG. 4, thermocouple well 128 is 0.64cm diameter stainless steel tubing that is inserted into the center of a4 cm diameter stainless steel vacuum casing 88. A thermocouplepositioned within thermocouple well 128 may be used to monitor thetemperature of heater element 84 adjacent to casing 88.

Dry fill material may need to be packed within a well in a substantiallyuniform manner. Dry fill material may need to be used to avoid formationof gaps and/or settling of the fill material when water within the fillmaterial evaporates. If a gap exists within the fill material, a leg ofthe heater element may expand into the gap when the heater elementexpands. If a leg of a heater element expands into a gap, the leg maycontact or approach the opposite leg of the heater element. If the legcontacts the opposite leg, the heater element may short and fail. If theleg approaches the opposite leg, electricity may arc to the opposite legand cause the heater element to fail.

If heater element 84 is a radiant heating element, the heater elementmay include top 130 as depicted in FIG. 12. Top 130 may thread ontoheater casing 94 near ground surface 52, as shown in FIGS. 6, 8, and 9,or the top may be welded to the heater casing, to form a wellhead forthe heater element. If the casing is an enclosed heater casing 94, asshown in FIG. 6, the casing may be filled with a gas. In someembodiments, the gas may enhance thermal conduction between heatingelement 84 and casing 94 to improve heating response time during initialheating. In some embodiments, the gas may be a corrosion inhibiter. Asshown in FIG. 12, top 130 may include openings 132. A fill tube may beplaced in a first opening and the gas may be flowed into casing 94. Gasoriginally in casing 94 may flow out of the second opening. When thedesired gas fills casing 94, the second opening may be plugged, the tubemay be removed, and the first opening may be plugged.

If heating element 84 is to be placed in an open wellbore, as depictedin FIG. 9, cement 134 or another type of securing method or device mayfix casing 94 to soil 34. Top 130 may be threaded or welded to casing94.

FIG. 13 shows a plan view of an embodiment of a layout for heaterelements 84 positioned within trenches. Heater elements 84 placed intrenches may be placed in long rows. For heater elements 84 thatconductively heat adjacent material, more than one heater element may beplaced in a single trench as long as a distance between heater elements,fill material, or spacers ensures that the heater elements will nottouch or be close enough to each other to arc. For heater elements thatradiatively heat a heater casing, more than one heater element may beplaced within a single heater casing. Heater elements 84 may be placedin trenches that were formed by a trenching machine. After heaterelements 84 are positioned within trenches and electrically coupled to apower source, cuttings formed when making the trench may be used to fillthe trenches. A vacuum system may be installed, a cover may be placedover the treatment area, and the system may be energized. Heaterelements placed in trenches may be used in ex situ applications or totreat low depth soil contamination in situ that is within about 2 m of asoil surface. Heater elements positioned in trenches may have longlengths that span across contaminated soil 106. In certain embodiments,rows of heater elements 84 may be separated by distances equal to abouttwice the insertion depth of the heater element into soil 34. Heaterelements may be placed in casing laid in trenches and exiting at thesurface, thereby allowing replacement of heater elements.

As shown in FIG. 10, heater element 84 may be placed in soil 34 so thata portion of heater section 114 is below contaminated soil 106, and aportion of the heater section is above the contaminated soil. Theportion of heater section 114 below contaminated soil 106 may be 1 m ormore in depth. Heating a section of uncontaminated soil 104 belowcontaminated soil 106 may prevent a falloff in temperature at interface102. The cross-sectional area of heater element 84 adjacent tocontamination interface 102 may be small, or may be made of a differentmaterial, so that more heat is diffused into the soil adjacent to theinterface. Diffusing more heat adjacent to the interface may promote amore uniform temperature distribution throughout contaminated soil 106.

To implement a soil remediation process, such as the process depicted inFIG. 1, wells may be positioned in the soil. The wells may be installedby placing wells within drilled openings, by driving and/or vacuumingwells into the ground, or by any other method of installing wells intothe soil. The wells may be extraction wells 32, heat injection wells 36,fluid injection wells 38, and/or test wells 40. A ring or rings ofdewatering wells may be installed around a perimeter of the area to betreated. The dewatering wells may be operated to remove water from thetreatment area and to inhibit water inflow into the treatment area. Insome embodiments, extraction wells, and/or fluid injection wells (andpossibly other types of wells) may be connected to dewatering pumps sothat the treatment area is rapidly and efficiently dewatered.

Heat injection wells 36 and extraction wells 32 that include heaterelements may be coupled to controllers (if necessary) and to powersource 76 or power sources. Extraction wells 32 may be coupled to vaporcollection system 46. The vapor collection system 46 may be connected totreatment facility 44. Other wells, such as fluid injection wells 38 andtest wells 40, may be coupled to appropriate equipment. In someembodiments, treatment facility 44 may be engaged to begin removingoff-gas from soil 34. Heat injection wells 36 and extraction wells 32that include heater elements may be energized to begin heating soil 34.The heating may be continued until the soil reaches a desired averagetemperature for a desired amount of time. The desired averagetemperature may be slightly higher that the boiling point of a highboiling point contaminant within soil 34. A desired average temperaturemay be over 100° C., 400° C., 600° C., or higher. A desired amount oftime may be days, weeks, months or longer. The desired amount of timeshould be sufficient to allow for contaminant removal from soil 34.

A remediation site may be an area at or near an original location of thecontaminated soil. For ex situ applications, contaminated soil may becollected from one or more locations and transported to one or moreremediation sites. Collection may include excavation and transportationusing conventional earth moving equipment.

In some embodiments, contaminated soil may be arranged in long,substantially rectangular piles. A remediation site may include morethan one pile of soil. For example, a remediation site may include twoto four piles of contaminated soil. A pile may have a volume of about2,000 to about 5,000 m³. In an embodiment, a pile may have a height ofabout 3 m, a width of about 8 m, and a length of about 35 m.Alternatively, a pile may have a height of about 3 m, a width of about25 m, and a length of about 100 m. In an embodiment, a verticalcross-sectional shape along a width of a soil pile may be substantiallytrapezoidal.

Heaters may be placed horizontally in a pile of contaminated soil byembedding the heaters in a portion of soil, placing the heaters intrenches formed in the soil, and/or forming layers of heaters betweenlayers of contaminated soil. Alternatively, a heater elements may beplaced in casing or tubing, at least one end of which extends to thesurface to allow replacement of the heater element. In an embodiment, afirst layer of soil may be placed in a pile and leveled using equipmentincluding, but not limited to, small earthmovers, bulldozers, and frontend loaders. Heaters may be placed on the soil. The heaters may be longstrips of a stainless steel. Ends of the heaters may be coupled to apower source that supplies electricity to the heaters to resistivelyheat the heaters when initiated. Additional soil may be placed on top ofthe heaters and leveled. Additional heaters and soil may be installed tocomplete the pile. The heaters may be spaced relatively close together(e.g., about 1 m apart) to allow for rapid heating of soil in the pile.Vapor extraction wells may be placed in desired locations in the pile,and/or a vapor extraction system may be formed adjacent to the pile.

A cover may be placed over the pile, vacuum may be initiated, andheating of the soil may be initiated. The cover may be flexible toaccommodate subsidence of the soil level in the pile due to vacuum andremoval of material from the soil (e.g., water and contaminants).

In addition to allowing removal of contaminants from the soil, heatingthe soil may result in the destruction of contaminants in situ.Superposition of heat from a plurality of heaters used to radiativelyand/or conductively heat soil at a treatment site may raise thetemperature of the soil throughout the treatment site above temperaturesthat will allow for reaction of contaminants. The presence of anoxidizing agent, such as air, may result in the oxidation ofcontaminants that pass through the heated soil. In the absence ofoxidizing agents, contaminants within the soil may be altered bypyrolysis. Vacuum applied to the soil may remove some reaction productsfrom the soil.

Many soil formations are characterized by a relatively large weightratio of water to contaminants within the soil. Raising the temperatureof the soil to a vaporization temperature of water or above may resultin vaporization of water in the soil. The water vapor may vaporizeand/or entrain contaminants within the soil. Vacuum applied to the soilmay remove water vapor and contaminants entrained within the water vaporfrom the soil. Vaporization and entrainment of contaminants in watervapor may result in the removal of medium and high boiling pointcontaminants from the soil.

For deep contamination, heater wells may be arranged vertically within apile of contaminated soil to supply heat to the soil. Some heater wellsmay include perforated casings that allow fluid to be removed from thesoil. A heater well with a perforated casing may also allow fluid to beinjected into the soil. Vacuum may be applied to the soil to draw fluidfrom the soil. The vacuum may be applied at the surface and/or throughvapor extraction wells placed within the soil.

FIG. 14 depicts a vertical cross section along a substantiallytrapezoidal width of pile 136 of contaminated soil 106. Sloping surfacesof pile 136 may promote stability of the pile. A long axis of casedheaters 138 and/or heater/vapor extraction wells 140 may besubstantially parallel to a length of pile 136. In an embodiment inwhich a length of pile 136 substantially exceeds a width and a height ofthe pile, placing cased heaters 138 and/or heater/vapor extraction wells140 lengthwise within the pile may reduce a number of wells required toremediate a given volume of soil. One or more injection wells 142 mayalso be placed lengthwise within pile 136.

A liner may be placed or assembled on a ground surface at a remediationsite before a pile of contaminated soil is formed. The liner may inhibitfluid (e.g., air and/or water) from entering the pile duringremediation. The liner may inhibit fluid (e.g., off-gas) from escapingto the environment from the pile. In an embodiment, a bottom portion ofthe liner may be high temperature resistant plastic and/or metal. Thesheeting may be sealed together. A bed of gravel or sand may be placedon top of the sheeting to provide a level surface and to insulate thesheeting from heat applied to soil in the pile during remediation.

As shown in FIG. 14, liner 144 may be placed on ground surface 52 ofuncontaminated soil 104 before pile 136 of contaminated soil 106 isformed. Alternatively, porous layer 146 may be placed between liner 144and contaminated soil 106. Porous layer 146 may include a freelydraining material such as sand or gravel. Collection conduit 148 may beplaced in porous layer 146 to collect drainage from contaminated soil106 of pile 136. Collection conduit 148 may be connected to acontaminant treatment system.

Sealing sheet 150 may be placed on or above contaminated soil 106 ofpile 136. Sealing sheet 150 may be substantially impermeable to airand/or liquid. Sealing sheet 150 may be flexible. In some embodiments,sealing sheet 150 may be a carbon steel plate or sheet that is weldedtogether. If the soil to be remediated will generate corrosivechemicals, a sealing sheet may be made of a more chemically resistantmetal than carbon steel. For example, sealing sheet 150 may be made of316 stainless steel that is more resistant to hydrochloric acidcorrosion and other corrosive chemicals than carbon steel if thecontaminated soil contains chlorinated compounds that will decompose toform hydrogen chloride and/or other corrosive compounds. In someembodiments, corrosive chemicals may react with clay or other componentsof the soil to effectively destroy the corrosive chemicals. Corrosivechemical generation may not be a problem in such embodiments.

A soil remediation site may include insulation 152 and/or cover 154.Insulation 152 may inhibit heat loss to the environment. In anembodiment, insulation 152 may be mineral wool. Alternatively, a layerof sand or gravel or lower conductivity cement may be used to spacesealing sheet 150 away from high temperatures. Cover 154 may inhibitwater from entering into pile 136. In some embodiments, cover 154 mayserve as a barrier to inhibit vapor loss from the remediation site.Cover 154 may be, but is not limited to, a rain tarp made of waterprooflightweight fabric, plastic sheeting, and/or sheet metal. Cover 154 maybe positioned over pile 136. In some embodiments, cover 154 may besealed to the ground and/or to remediation equipment or structures. Inan embodiment, cover 154 may be positioned over contaminated soil 106and fixed to ground surface 52. In other embodiments, cover 154 may bepositioned on top of insulation 152 over contaminated soil 106 and fixedto ground surface 52.

Contaminated soil in a pile may be at least partially contained withbarriers along at least a portion of a perimeter of the contaminatedsoil. The barriers may form a retaining structure. Retaining structuresmay include, but are not limited to, natural soil layers that aresubstantially impermeable, walls of a tank, and/or walls of a man-maderemediation pit. Retaining structures may be used advantageously forremediation of soil that contains potentially explosive contaminants. Insome embodiments, retaining structures and materials may be reused forsubsequent treatment of contaminated soil.

FIG. 15 depicts pile 136 of contaminated soil at least partiallysurrounded by retaining structure 156. In an embodiment, retainingstructure 156 may include concrete retaining walls. In some embodiments,one or more retaining walls may be formed of assembled sections.Sections may be disassembled and moved to facilitate insertion andremoval of soil and connection of central remediation system equipment(e.g., power and vacuum sources). Retaining structure 156 may include abase, such as a concrete slab. Retaining structure 156 may be at leastpartially surrounded by insulation 152. In an embodiment, insulation 152may be styrofoam insulation. In some embodiments, an inner surface ofthe side walls may be insulated with materials such as firebrick toinhibit thermal degradation of the side walls during remediation ofcontaminated soil.

In an embodiment, one or more of side walls of retaining structure 156may include openings that allow for passage of monitoring equipment andheaters and/or vacuum system equipment into soil 106. Soil 106 inretaining structure 156 may be leveled before introduction of heatersand/or vacuum system equipment. In an embodiment, soil 106 may beleveled by earthmoving equipment lowered into in retaining structure 156by a crane. In some embodiments, bare heaters 158, cased heaters 138,heater/vapor extraction wells 140, and injection well 142 may be placedas shown in FIG. 15. A horizontal spacing between heaters and wells maybe about 1 m to about 2 m. A vertical spacing between heaters and wellsmay be about 1 m. Collection conduit 148 may be placed in porous layer146. A bottom row of heaters and wells may be spaced about ⅓ m above atop of porous layer 146. Sealing sheet 150, insulation 152, and cover154 may be placed on top of contaminated soil 106 and/or coupled toretaining structure 156. A top row of heaters and wells may be spacedabout ⅓ m below sealing sheet 150.

Other types of barriers may be placed around a contamination site toprovide at least partial containment of contaminated soil. U.S. Pat. No.6,419,423 to Vinegar et al., which is incorporated by reference as iffully set forth herein, describes a barrier for an in situ soilremediation system. A barrier may be metal plates driven into the soilaround a perimeter of a contaminated soil region. In other embodiments abarrier may be, but is not limited to, a grout wall formed in the soil,and/or a frozen barrier formed by freeze wells spaced around a treatmentarea.

A remediation site, such as pile 136 shown in FIGS. 14 and 15, mayinclude one or more vacuum ports. A vacuum port may extend through andbe sealed to sealing sheet 150. The vacuum port may be coupled withcontaminated soil 106. Air and vapors may be removed from soil 106through the vacuum port. Air and vapors from soil 106 may be conductedfrom the vacuum port to a treatment system or treatment facility. Vaporsmay also be removed from contaminated soil 106 through a conduit. Insome embodiments, a conduit may be coupled to a lower portion of pile136. A ventilating layer below contaminated soil 106 in pile 136 mayallow vapors to be drawn from contaminated soil 106 into the conduit.The ventilating layer may be a perforated plate. Vapors fromcontaminated soil 106 may be transported through the conduit to atreatment facility.

In some soil remediation system embodiments, a treatment system forprocessing off-gas from contaminated soil may include a thermal oxidizeror reaction system for destroying contaminants in an off-gas stream fromsoil remediation. The thermal oxidizer may heat the off-gas to a hightemperature to destroy some contaminants within the off-gas. The use ofthermal oxidizers may be minimized and/or eliminated due to the largecosts associated with purchase, transportation, and operation of thermaloxidizers. At some soil remediation sites, the use of thermal oxidizersor other types of reactors may not be as practical as, for example,absorbent carbon beds.

Processing of a pile of soil at a remediation site may be achieved usinga central power supply, a central off-gas treatment system, and centralinstrumentation and power control systems. As a pile of soil is formed,wells (e.g., heater wells and vapor extraction wells) and conduit may beplaced in the soil and coupled to central equipment for remediation.After remediation, central equipment may be uncoupled from wells andconduit in the pile before removal of the treated soil. In an embodimentin which a pile of contaminated soil is partially contained by endwalls, such as buttressed concrete end walls, central equipment may becoupled to wells and conduit in the soil through an end wall. In someembodiments, all or part of a horizontal layer of wells may bestructurally coupled together. The wells may be moved as a unit usingmoving equipment (e.g., a crane).

Several piles of contaminated soil may be formed at a remediation siteto process contaminated soil. In some embodiments, piles may be treatedsequentially for efficient use of available power and central equipment.For example, a first pile of contaminated soil may be prepared. A vacuummay be drawn on the first pile and heating of the first pile may beinitiated. While the first pile is heating, a second pile may be formed.When processing of the first pile is complete, a central power supplymay be decoupled from heaters in the first pile, and the power supplymay be coupled to heaters in the second pile. Heating of the second pilemay be initiated. In some embodiments, heat of the first pile may betransferred to the second pile to facilitate heating of the second pile.A third pile of contaminated soil may be formed for processing whenremediation of soil in the second pile is completed. When soil in thethird pile is processed, processed soil in the first pile may be removedand replaced by a new batch of contaminated soil. A cycle of use of thefirst pile, the second pile, and the third pile may be repeated tocomplete remediation of all contaminated soil. In an embodiment, thenumber of piles used at a remediation site may range from two to six.

In certain embodiments, placement of heaters and vapor extraction wellsmay result in partial removal of contamination from bottom edge portions(“fringe area”) of the pile. After treatment of a pile of soil, soilfrom a fringe area of the pile may be treated as part of anothercontaminated pile formed subsequently.

In some embodiments, a first heated soil pile may be used to destroycontaminants in an off-gas stream from soil in a second pile undergoingremediation. In some embodiments, a thermal oxidizer or other reactormay be used to process contaminants removed during remediation of soilin a first pile. In other embodiments, soil in a first pile may besubstantially uncontaminated so that a treatment facility without athermal oxidizer or other reactor is able to handle contaminants in anoff-gas stream removed during remediation. For example, soil in a firstpile may originate from a fringe area of soil contamination.

Soil in a first pile may be heated and remediated. After remediation,heaters may maintain a high temperature within the first pile, and avacuum may be maintained on the first pile. Remediation of soil in thefirst pile may result in soil that is permeable and at a hightemperature. In some embodiments, a soil-filled roll off container maybe used instead of a first pile of soil. A second pile of contaminatedsoil may be formed. The second pile of contaminated soil may be formedduring remediation of the first pile. Vapor extraction wells of thesecond pile may be coupled to injection wells of the first pile. In someembodiments, a blower or other drive system may be coupled betweenextraction wells of the second pile and injection wells of the firstpile to facilitate movement of off-gas from the second pile to the firstpile. The second pile may be heated and remediated. Off-gas from thesecond pile may be directed through injection wells into the heatedfirst pile. A portion of contaminants from the second pile may bedestroyed by pyrolysis reactions or oxidation reactions in the firstpile. Some of the pyrolysis reactions and/or oxidation reactions may beexothermic reactions that facilitate maintenance of a high temperaturein the first pile. Vacuum drawn on the first pile may draw off-gas fromthe first pile to a treatment facility.

In some soil remediation system embodiments, a soil treatment site maybe a long, substantially rectangular remediation pit. For example, asoil remediation pit may be a concrete lined pit that is about 100 mlong, about 30 m wide and about 2 m deep. Remediation pits having longeror shorter lengths, widths, and/or depths may also be used. Several soilremediation pits may be in use at a remediation site.

FIG. 16 depicts an embodiment of soil remediation pit 160. Contaminatedsoil 106 may be at least be partially contained in remediation pit 160.Remediation pit 160 may be prepared such that leaching of contaminantsfrom soil 106 into surrounding soil and/or migration of contaminantsfrom the soil is minimized or prevented. Remediation pit 160 may be anexcavated area. Sides of a remediation pit may be lined with thermalinsulation 162. Thermal insulation 162 may minimize heat loss tosurrounding soil 34 during treatment of contaminated soil 106. Thermalinsulation 162 may reduce heat loss from contaminated soil 106, therebyeffectively increasing a heating rate of the soil. Thermal insulation162 may include, but is not limited to, cement, sand, and/or firebrick.

Remediation pit 160 may also include vapor seal 164 at least partiallysurrounding thermal insulation 162. Lower sealing sheet 166 may beplaced on surface 52 of soil 106. Lower sealing sheet 166 may beflexible to accommodate settling of the soil due to compaction and/ormaterial removal (e.g., water and/or contaminants) during a remediationprocedure. Lower sealing sheet 166 may be substantially impervious toair and/or liquid.

In some embodiments, heaters 168 may be placed on top of lower sealingsheet 166. Heaters 168 may heat soil 106. Seal 170 may be positionedaround a perimeter of remediation pit 160. Seal 170 may be positioned ona surface of vapor seal 164 to provide an edge seal for heaters 168and/or lower sealing sheet 166. Seal 170 may be inflatable rubber tubingto allow sealing of irregular surfaces. Seal 170 may be positioned farenough away from heaters 168 to avoid heating of the seal. Remediationpit 160 may be covered at least partially with insulation 152 to inhibitheat loss to the environment. In an embodiment, insulation 152 may bemineral wool. Upper sealing sheet 172 may be placed between heaters 168and insulation 152.

Cover 154 may be positioned over insulation 152. Cover 154 may inhibitwater from entering into remediation pit 160. In some embodiments, cover154 may serve as a barrier to inhibit vapor loss from the remediationsite. Cover 154 may be, but is not limited to, a rain tarp made ofwaterproof lightweight fabric, plastic sheeting, and/or sheet metal.Cover 154 may be positioned over remediation pit 160. In someembodiments, cover 154 may be sealed to the ground and/or to remediationequipment or structures. In an embodiment, cover 154 may be positionedover contaminated soil 106 and fixed to ground surface 52. In otherembodiments, cover 154 may be positioned on top of insulation 152 overcontaminated soil 106 and fixed to ground surface 52.

A remediation site may include one or more vacuum ports 174. Vacuum port174 may extend through and be sealed to sealing sheets 166, 172. Air andvapors may be removed from soil 106 through vacuum port 174. Air andvapors from soil 106 may be conducted from vacuum port 174 to atreatment system or treatment facility. Vapors may also be removed fromcontaminated soil 106 through conduit 176. In some embodiments, conduit176 may be coupled to a lower portion of remediation pit 160.Ventilating layer 178 below soil 106 in remediation pit 160 may allowvapors to be drawn from contaminated soil 106 into conduit 176.Ventilating layer 178 may be a perforated plate. Vapors from soil 106may be transported through conduit 176 to a treatment facility.

In an embodiment of a remediation system, conduit 176 may be attached toa fluid supply. Fluid may be introduced into contaminated soil 106through conduit 176. The fluid may be, but is not limited to, steam orliquid water, a solvent, a surfactant, a chemical reactant such as anoxidant, a biological treatment carrier, a drive fluid, and/or a heattransfer fluid. A solvent or surfactant may be used to increase fluidflow through contaminated soil 106 toward vacuum port 174. A reactantmay react with contaminants to destroy contaminants and/or convertcontaminants into volatile reaction products. The reaction products maybe removed from the soil through vacuum port 174. A drive fluid may beused to move contaminants entrained in vapors toward vacuum port 174. Aheat transfer fluid may be used to promote convective transfer of heatthrough the soil.

In some embodiments, a first conduit or conduits may allow a vacuum tobe drawn on soil in a remediation pit from below the remediation pit. Asecond conduit or conduits may allow for fluid insertion into theremediation pit from below the soil in the remediation pit. Aremediation system with a first conduit or conduits for drawing a vacuumand a second conduit or conduits for inserting fluids may allow fordrawing a vacuum on a remediation pit and for inserting fluid into aremediation pit without the need to change equipment during aremediation process.

Contaminated soil may be placed into tanks. FIG. 17 depicts anembodiment of contaminated soil 106 in tank 180 for ex situ remediationof the soil. Tank 180 may be formed on base 182. In an embodiment, base182 may be made of a rigid, substantially impermeable substance such asconcrete. Base 182 may serve as a lower insulation layer for tank 180.Tank 180 may include an outer lining or shell 184. The annular spaceformed between inner lining 186 and shell 184 may be filled with thermalinsulation 162. Thermal insulation 162 may be, but is not limited to,cement, sand, firebrick, and/or mineral wool.

In some embodiments, ventilating layer 178 may be located on or adjacentto a surface of soil 106. Vapor extraction well 188 may be coupled tothe space above ventilating layer 178 so that the vapor extraction wellis able to draw vacuum on soil 106 below the ventilating layer. In anembodiment, vapor extraction well 188 may be a heater/vapor extractionwell. Vapors may be conducted through ventilating layer 178 toward vaporextraction well 188. In an embodiment, a vacuum source may draw vaporsthrough ventilating layer 178 toward vapor extraction well 188.Ventilating layer 178 may be, but is not limited to, a grating,perforated sheet metal, and/or chain-link fence. An outer casing ofvapor extraction well 188 may be perforated to allow vapors to enter thewell and be removed by the vacuum source. The vapors may be conductedfrom vapor extraction well 188 to a treatment facility. Sealing sheet150 may be placed between ventilating layer 178 and insulation 152 abovesoil 106 to serve as a vacuum seal.

In some embodiments, heater wells may be arranged substantiallyvertically within soil 106 in a regular or substantially regularpattern. For example, heater wells may be arranged in a hexagonalpattern around vapor extraction well 188 within contaminated soil 106 intank 180. In some embodiments, heater wells and/or vapor extractionwells may be slanted or placed substantially horizontally in the soil.Heater wells 190 and vapor extraction well 188 may extend through precutholes in ventilating layer 178, sealing sheet 150, and insulation 152above soil 106. Sealing sheet 150 may be sealed to top hats of heaterwells 190 and vapor extraction wells 188. Allowances in heater wells,vapor extraction wells, and seals of the wells to sealing sheet mayallow for thermal expansion and for shrinkage of soil due to materialloss (e.g., water loss). Sealing sheet 150 may be sealed to tank 180.Depending on the temperature to which the seals will be subjected, theseals may be formed of rubber, silicone, and/or metal welds.

Clean soil may be used as insulation around retaining structures. Forexample, a clean soil berm may be formed around tank 180. In anembodiment, a clean soil berm may surround shell 184. A clean soil bermmay also be used as thermal insulation 162 between lining 186 and shell184. When soil 106 is heated, a portion of the berm adjacent to tank 180may dry out. The dry soil may act as insulation for tank 180. In someembodiments, insulation may be coupled to outer surface of shell 184.

FIG. 18 depicts an embodiment of a portion of a remediation system thatincludes risers 192. Risers 192 may be used to remediate soil thatcontains dense non-aqueous phase liquids that have medium to highboiling points and do not significantly thermally degrade attemperatures used during remediation. For example, risers may be used ina soil remediation system for remediating soil contaminated withmercury. In an embodiment, riser 192 is a heated riser. Riser 192 may becoupled to sealing sheet 150 above ventilating layer 178. A portion ofvapor extraction well 188 that extends above soil 106 may be a riser.Insulation 194 may cover a portion of riser 192. In an embodiment,insulation 194 may cover ascending portion 196 of riser 192. Ascendingportion 196 may be heated with heater 198 to a temperature greater thana boiling point of a contaminant to be removed from the soil. Heatsupplied by heater 198 may inhibit condensation of the contaminant inriser 192.

Conduit 176 exiting riser 192 may conduct vapor removed from soil to atreatment facility. Conduit 176 may be coupled to a vacuum system. Insome embodiments, all or portions of conduit 176 may not be insulated.Vapor may be allowed to condense within conduit 176. Conduit 176 may bemaintained at a temperature sufficient to inhibit formation of solids inthe conduit. Riser 192 may have sufficient height so that a slope ofconduit 176 towards a treatment facility will facilitate flow of anycondensed liquids in the conduit to the treatment facility.

A soil remediation site may include at least two treatment sites. In asoil remediation embodiment, at least a portion of the vapors producedby heating soil at a first treatment site may be used to provide heat tocontaminated soil at a second treatment site. FIG. 19 depicts anembodiment of a soil remediation site including two treatment sites.Remediation site 200 may contain soil 106 and remediation site 200′ maycontain soil 106′. In an embodiment, site 200 and/or site 200′ may be,for example, a remediation pit or a pile of soil. When soil 106, 106′ isinitially placed in sites 200, 200′, soil 106 may contain substantiallythe same contaminants or different contaminants than soil 106′. Sites200, 200′ may be coupled together by conduits. Valve system 202 may beused to control flow of fluids between sites 200 and 200′ throughconduits 176, 176′, and 204. Valve system 202 may include a valve inconduit 176 from site 200, a valve in conduit 176′ from site 200′, and avalve in other conduits 204 at the remediation site. Valve system 202may be located in a readily accessible portion of the remediation site.

Conduits 176, 176′ are shown schematically in FIG. 19 as single pipesentering/leaving sites 200, 200′. In a remediation system, conduits 176,176′ may be a plurality of conduits that enter/leave sites 200, 200′ atseveral locations. In an embodiment, conduits 176, 176′ may enter/leavea manifold adjacent to valve system 202.

Soil 106 in site 200 may be heated with heaters 168. Heaters 168 may belocated in soil 106, above the soil, and/or below the soil. Valve system202 may be set to inhibit fluid transfer from site 200 to site 200′during heating of soil 106 in site 200. A vacuum source may be used toapply a vacuum through vacuum port 174 during heating and remediation ofsoil 106. In some embodiments, vacuum may also be drawn through conduits176, 204 to remove vapor from site 200. After contaminated soil 106 insite 200 is treated, heaters 168 may be turned off. After heaters 168are turned off, application of the vacuum may be discontinued.Subsequently, valve system 202 may be set to connect sites 200 and 200′.A vacuum source may be coupled to vacuum port 174′ in treatment site200′. Air may be introduced at vacuum port 174 and allowed to flow downthrough soil 106 and through conduits 176, 176′ to site 200′. Air movingthrough site 200 may be heated by soil 106. The heat of the air maytransfer to soil 106′ in treatment site 200′. Heat transfer to airpassing through soil 106 in treatment site 200 may cool soil 106.Heaters 168′ may be used to supply additional heat to soil 106′ in site200′. Transferring heat from site 200 to site 200′ may substantiallyreduce the amount of energy needed to be supplied to soil 106′ fromheaters 168′. Transferring heat from site 200 to site 200′ maysubstantially reduce the amount of time needed to cool soil 106 so thatthe soil is cool enough to process (e.g., move to a new location).

In some process embodiments, conduit 204 may be attached to a fluidsupply to introduce fluid into soil 106 in site 200 or soil 106′ in site200′. In some process embodiments, conduit 204 may be connected to avacuum system to draw fluid out of soil 106 and/or soil 106′. Fluidintroduced into soil 106 and/or soil 106′ may be used to treat the soilin site 200 and/or site 200′. The fluid may be used to move contaminantswithin soil 106 and/or soil 106′ to facilitate remediation.Additionally, the fluid may be used to assist the transfer of vaporsbetween site 200 and site 200′. Valve system 202 may be set to directfluid to site 200 and/or site 200′. For example, valve system 202 mayallow fluids to enter site 200 through conduits 204 and 176 duringheating and remediation of soil 106. Vacuum applied through vacuum port174 may draw fluid into soil 106. Valve system 202 may be set to preventfluid from entering site 200 after soil 106 is fully treated. Ifrequired, additional “block and blend” valve arrangements may beinstalled to positively inhibit back flow of fluids into previouslycleaned soil. After treatment of site 200, valve system 202 may beadjusted to allow fluid to flow from site 200 to site 200′. Duringremediation of contaminated soil 106′ in site 200′, valve system 202 maybe positioned to allow fluid to enter site 200′. In some embodiments, apump may be coupled to conduit 204 to force fluid into soil 106 and/orsoil 106′.

In an embodiment, heated soil at one site may be used to at leastpartially destroy contaminants in vapors produced from soil at anothersite. Soil 106 in site 200 may be thermally remediated to remove orreduce contamination within the soil. Soil in site 200 may be heated toa high temperature. The temperature may be sufficient to allow forpyrolysis, oxidation, or other chemical reaction of contaminants withinvapor that are drawn through the soil. In some embodiments, an averagetemperature of soil in site 200 may be less than about 200° C., lessthan about 300° C., less than about 400° C., less than about 500° C., orless than about 600° C.

After soil 106 in site 200 is raised to a desired temperature, heatingof soil 106′ in site 200′ may be initiated. Vapors removed from site200′ may be drawn by a vacuum through site 200. For example, in FIG. 19,valve system 202 may be set to allow a vacuum pulled through vacuum port174 to draw vapor from soil 106′ through conduits 176′, 176 and intosoil 106. If desired, a reactant such as an oxidant (e.g., air, oxygen,and/or hydrogen peroxide), or other chemical may be introduced into thevapor by setting valve system 202 to allow the reactant to be drawntoward soil 106.

In other embodiments, soil 106 initially heated at site 200 may becontaminated soil. Contaminants removed from the soil during heating maybe directed to a treatment facility. The treatment facility may includea transportable thermal oxidizer that destroys the contaminants. Whenthe soil is heated to the desired temperature, the thermal oxidizer mayno longer be needed to treat contaminants from soil being remediated.The thermal oxidizer may be removed. In some embodiments, soil 106 insite 200 may initially be uncontaminated or substantially uncontaminatedsoil that is heated to a high temperature. Uncontaminated orsubstantially uncontaminated heated soil 106 in site 200 may be usedtreat contaminants from soil 106′, thus reducing equipment requirementsof a coupled treatment facility.

Contaminants in the vapor from soil 106′ may be destroyed within heatedsoil 106 in site 200. In some embodiments, an oxidant or other reactantmay be drawn into site 200 to facilitate destruction of contaminants inheated soil. Reactions of contaminants from soil 106′ may be exothermicreactions that contribute to maintenance of high soil temperature insite 200. Soil 106 site 200 may be maintained at a high temperature.Heating soil 106 site 200 may result in the soil having a highpermeability and a large surface area. The heat and large surface areamay advantageously be used to destroy contaminants produced from asecond site, such as site 200′.

In certain embodiments, including the embodiment shown in FIG. 19, aconduit may be used to introduce a fluid (e.g., air) to a site toaccelerate heat transfer through contaminated soil at the site. Forexample, contaminated soil 106 in site 200 of FIG. 19 may be heated fromthe top with heaters 168 and heated from the bottom with heaters 206,until a desired temperature is established in the soil. Heaters 168 maybe turned off and air may be introduced to a lower portion ofcontaminated soil 106 through conduit 176. The air may draw heat fromheaters 206. As heat is transferred to the air, an injection rate ofheat from heaters 206 may be increased. The heated air may transfer theheat upward through contaminated soil 106. A vacuum source may becoupled to vacuum port 174. Air may be drawn through contaminated soil106 toward vacuum port 174. The vacuum may be used to control airflowthrough (i.e., the heating rate of) the soil. Use of a fluid (e.g., air)to transfer heat through contaminated soil 106 may reduce the energyrequirements for remediation of contaminated soil 106 in site 200.

In an embodiment, ex situ remediation may be used in conjunction with insitu soil remediation to remediate soil. For example, a heated zone ofsubsurface soil may be used as a site to at least partially destroycontaminants in vapors from another site. In other embodiments, soilfrom more than one location may be remediated at one treatment site.

FIG. 20 depicts an embodiment that may be used to remediate contaminatedsoil from more than one location simultaneously. Lower portion 208 ofcontaminated soil may be collected in remediation pit 160 for ex situremediation. Alternatively, lower portion 208 of contaminated soil maybe a location of subsurface contamination contained by barriers. Heaters210 may be placed above lower portion 208 of contaminated soil. Upperportion 208′ of contaminated soil may be placed above heaters 210.Heaters 210′ may be placed within upper portion 208′ of contaminatedsoil. Heaters 210, 210′ may include, but are not limited to, heaterblankets, strip heaters, and/or bare wires. Alternatively, heaters 210,210′ may be a horizontal arrangement of heater wells and/or heater/vaporextraction wells. Lower portion 208 and upper portion 208′ ofcontaminated soil at the site may be collected from more than onelocation and may contain substantially the same or substantiallydifferent contaminants. Sealing sheet 150, insulation 152 over soil, andcover 154 may be placed above upper portion 208′ of contaminated soil.Upper portion 208′ and lower portion 208 of contaminated soil, which mayoriginate from more than one location, may be heated with heaters 210,210′ at substantially the same time within remediation pit 160.

For deeper sites of contaminated soil, trenches may be formed in lowerportion 208 of contaminated soil, and heaters 210″ may be placed in thetrenches. Alternatively, remediation pit 160 may be partially filledwith contaminated soil. Heaters 210″ may be placed on the soil, and morecontaminated soil placed over the heaters. Alternatively, heater wellsand/or heater/vapor extraction wells may be arranged vertically withinlower portion 208 of contaminated soil and/or upper portion 208′ ofcontaminated soil.

A layered arrangement of heaters, as shown in FIG. 20, may be used toprovide relatively rapid and substantially even heating at a remediationsite. In an embodiment, two or more coupled remediation sites (e.g.,sites 200 and 200′ shown in FIG. 19) may be heated simultaneously withlayered arrangements of heaters.

Embodiments described herein may be used for high temperature removal ofcontaminants from contaminated soil at one or more sites. Hightemperature materials for heating and containing the contaminated soilmay be incorporated depending on the expected temperature requirementsand properties of the contaminants and vapors produced. Embodiments mayalso be used for low temperature dewatering of contaminated sludge.Steel tanks may be used for containing the contaminated sludge.Dewatering sludge may substantially reduce a volume of wet soil tofacilitate handling of the soil and contaminants within the soil.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as examples of embodiments. Elements and materials maybe substituted for those illustrated and described herein, parts andprocesses may be reversed, and certain features of the invention may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims.

1. A method, comprising: at least partially containing soil at aplurality of treatment sites, wherein the plurality of treatment sitescomprises at least a first site and a second site; and treating soil atthe plurality of treatment sites, wherein treating soil comprises:heating soil at the first site using a plurality of heat sourcespositioned in the soil at the first site; heating soil at the secondsite using a plurality of heat sources positioned in the soil at thesecond site; and allowing a portion of vapors produced from the secondsite to enter the first site such that contaminants in the portion ofvapors produced from the second site are at least partially destroyed atthe first site.
 2. The method of claim 1, further comprising applying avacuum to soil at the first site.
 3. The method of claim 1, whereinheating soil at the first site comprises remediating soil at the firstsite.
 4. The method of claim 1, wherein off-gas from the second site isdirected into the first site.
 5. The method of claim 1, furthercomprising removing off-gas from the first site.
 6. The method of claim1, further comprising drawing off-gas from the first site to a treatmentfacility.
 7. The method of claim 1, further comprising pyrolyzingcontaminants from the second site at the first site.
 8. The method ofclaim 1, further comprising oxidizing contaminants from the second siteat the first site.
 9. A method, comprising: at least partiallycontaining soil at a plurality of treatment sites, wherein the pluralityof treatment sites comprises a first site and other sites; and treatingsoil at the plurality of treatment sites, wherein treating soilcomprises: heating soil at the first site using a plurality of heatsources positioned in the soil at the first site; heating soil at theother sites using a plurality of heat sources positioned in the soil atthe other sites; and allowing a portion of vapors produced from theother sites to enter the first site such that contaminants in theportion of vapors produced from the other sites are at least partiallydestroyed at the first site.
 10. The method of claim 9, furthercomprising applying a vacuum to soil at the first site.
 11. The methodof claim 9, wherein heating soil at the first site comprises remediatingsoil at the first site.
 12. The method of claim 9, wherein off-gas fromat least one of the other sites is directed into the first site.
 13. Themethod of claim 9, further comprising removing off-gas from the firstsite.
 14. The method of claim 9, further comprising drawing off-gas fromthe first site to a treatment facility.
 15. The method of claim 9,further comprising pyrolyzing contaminants from the other sites at thefirst site.
 16. The method of claim 9, further comprising oxidizingcontaminants from the other sites at the first site.